The invention relates to a radial press for workpieces with rotationally symmetrical outside surface, with a
(a) A plurality of press jaws disposed in a circle around the axis of the workpiece outer surface, which are movable radially to this axis and whose outsides have at least two first planar controlling surfaces sloping with respect to the axis and disposed V-wise, which run between two parallel lateral guiding surfaces disposed on the press jaws, the bisector of the "V" being aligned radially and the surface normals passing through the centroids of the controlling surface intersecting the axis,
(b) Control bodies whose insides each have at least one likewise planar, second controlling surface cooperating with the corresponding controlling surfaces of the press jaws,
(c) A drive means producing the axial displacement of the control bodies relative to one another.
The term, "rotationally symmetrical outside surface," as used herein, is to be interpreted to mean workpiece shapes having circular cross sections and cross sections in the form of regular polygons, such as are found in hexagonal or octagonal rolled stock. The outside surfaces of the workpieces can at the same time be rectilinear in the axial direction, barrel-shaped, or stepped. Such workpiece surfaces can be accommodated by constructing the press jaws accordingly. A special field of application for which the subject matter of the invention is preferentially suited is the joining of hose fittings consisting of steel to flexible hoses, as well as the production of cable thimbles.
In a known radial press described in PCT application No. WO 81/03456, both the controlling surfaces of the press jaws and the controlling surfaces of the control bodies are conical surfaces or sectors of these conical surfaces. The controlling surfaces of the press jaws are sectors of truncoconical surfaces whose base surfaces, of equal size, are identical. Two intersecting generatrices of these conical surfaces consequently form a wide-open "V" whose bisector is precisely radial to the axis A of press and workpiece.
As a rule, one of the two control bodies is fixed, and the other control body is displaced axially by a hydraulic drive against the fixed control body. Due to the above-described configuration of all controlling surfaces, the press jaws cover exactly half of the distance in the axial direction which is covered by the moving control body. It is apparent that a precisely full-surface contact between the cooperating controlling surfaces is possible only in one very specific axial position. Above and below this point of full-surface contact, contact takes place only along a central generatrix of the controlling surface of the press jaw, or along the two farthest outside longitudinal edges of the controlling surface of the particular press jaw. This peculiarity of conical controlling surfaces brings it about that, at high press forces, such as those occurring especially in the pressing of hose fittings, extremely high surface loading occurs, and resulting frequency in the breakdown of the lubricant film, so that a stiffness or low efficiency of the press is the result. Consequently, due to the response of an overload protection (pressure relief valve in the hydraulic drive), the operation of the press comes to a halt before the pressing operation has reliably been completed. Later this can endanger personnel, considering that hydraulic hoses with their fittings can be subjected to internal pressures of 1000 bars and more.
To forestall excessive wear due to the extreme line-of-contact pressures, the motion controlling surfaces are, as a rule, hardened. This requires either the use of materials that can be hardened on-site, or the use of materials which can be case-hardened by a so-called "pack hardening" process through diffusion into the surface at high temperatures. This heat treatment, which is necessary in any case, regularly results in a distortion of the workpieces, which has to be minimized by complex design measures, and the distortion, which can not be entirely avoided, must be compensated by grinding to dimension. Such materials, and their manufacturing and processing, are expensive and complicated, and even so they do not bring the desired success in every case.
Also, on account of the transition from line contact to surface contact to line contact, instabilities occur in the pressing process between the cooperating motion controlling surfaces. On the one hand when the press jaws make contact along their center lines they tend to rock about these lines so that the pressing results on the finished workpiece are not always precisely the same, and on the other hand the sliding of the press jaws on the motion control bodies is not uniform at both ends of the press jaws, so that the longitudinal axes of the press jaws are not always precisely parallel to the press axis.
The above-described instabilities can still be overcome to some extent as long as pressing at low pressing forces and/or small workpiece diameters is involved, as is the case in crimping operations in which a sheet metal fitting is pressed onto a low-pressure hydraulic hose with the formation of serrations. At high press pressures, therefore, the initially described, double-sided pressing jaws have, as a rule, been avoided, and instead pressing jaws that act unilaterally have been used, which are operated by a single motion control body and are supported for radial displacement on the face end of an anvil on which they are mounted for radial movement, with the aid in some cases of dovetail guides.
If the radial dovetail guides are not used, and conical motion controlling surfaces are used, the disadvantage is encountered that the press jaws have the tendency to distribute themselves irregularly on the circumference of the workpiece, so that the so-called "pressing center," i.e., the sum of the vectors of all individual forces no longer coincides with the press axis. This too leads to irregular results. The return springs usually used for spreading the press jaws apart cannot, in any case, prevent the unequal distribution of the press jaws.
Furthermore the useful stroke, in the case of press jaws operated by a motion control body, is shorter, because the press jaws are given a tilting stress by the shifting attack of the motion control body, so that a relatively great overlapping of the motion controlling surfaces is necessary.
To the extent that multilaterally operating presses are disclosed by U.S. Pat. No. 4,535,689 (FIGS. 18 and 19), the planar motion controlling surfaces of the press jaws are formed by the surfaces of wedge-shaped bodies which engage one another alternately from opposite directions and are guided in face-end plates of a press frame. Due to the alternate engagement of the wedges a considerable amount of motion control area is lost, i.e., the press jaws are supported by the wedges on no more than half of their outer surfaces, so that, at a given pressing force, at least twice the pressure per unit area occurs. The guidance in the press frame is only indirect, in a kind of overhung mounting, so that the lateral guidance is but slight in spite of the enormous amount of space required by the arrangement. The axis-parallel contact surfaces for the wedges provide the press jaws in any case with no kind of lateral or transverse guidance. In the given manner of construction it is not possible to arrange more than four pairs of motion control wedges or more than four press jaws around the workpiece. Lastly, maintenance is also problematical, since the lubrication points are very much concealed, so that the press has to be at least partially disassembled for lubricating purposes.
The invention is therefore addressed to the object of improving a radial press of the kind described above such that its efficiency will be increased, that it will permit uniform pressures all the way to the end of the press action, and that both the manufacturing and the maintenance costs will be reduced accordingly.